1. Field of Invention
The invention relates to a feed system for a rotating cutting tool in accordance with the preamble of claim 1.
2. Description of Related Art
Feed systems of this kind are used in the series manufacture of case components, for instance of engine/transmission cases. The respective machining stations, for example transfer machines, fine-boring units, special machines, horizontal boring machines or machining centers are equipped with a feed system for boring tools in which the cutting tool is coupled with a work spindle of the machine tool via the feed system.
The feed system permits to compensate defects occurring during manufacture which may occur, for instance, due to the wear of cutting edges, cutting edge tolerance, adjusting errors or dimensional variations, caused by temperature changes of the machine, etc. Moreover the feed systems permit to form cylinder bores having most narrow tolerances or having bores the radius of which is variable in response to the boring depth (e.g. forming of chamfers, radii, recesses, convex, concave or tapered circumferential walls).
In the known system the cutting tools may be formed on different tool holding fixtures, for instance boring bars, so-called eccentric spindles or feeding heads.
In FIG. 1, which is referred to already in this place, a known feed system distributed by the applicant by the name "eccentric spindle" is shown. In this feed system a tool holding fixture 2 is arranged coaxially at an eccentric spindle 4 which, in turn, is rotatably supported in a work spindle 6. The axis of the eccentric spindle 4 is offset vis-a-vis the axis of the work spindle 6 by the measure e. I.e. by rotating the eccentric spindle 4 a cutting tool (not represented) held in the tool holding fixture 2 can be radially offset vis-a-vis the axis of the work spindle 6 and thus a feed motion can be performed.
In the known feed system the adjusting movement of the cutting edge with respect to the work spindle 6 is effected by means of a comparatively complex drive system the principal components of which are briefly described hereinafter.
The known drive system includes a servomotor 8 the output shaft 10 of which is connected to a circulating ball spindle indicated by the reference numeral 12 in FIG. 1. By the circulating ball spindle 12 the rotation of the servomotor 8 is converted into an axial movement by which an adjusting slide 14 is movable in axial direction, i.e. in parallel to the axis of the work spindle 6, in response to the control. In the adjusting slide 14 a connecting member 16 coupled to a connecting bar 18 is rotatably supported. The connecting bar 18 is guided to be axially movable in the work spindle 6. Between the end portion of the connecting bar 18 on the side of the tool holding fixture and the adjacent end portion of the eccentric spindle 4 guided in the work spindle 6 there is disposed a lift-off rotary transformer 20 via which the axial movement of the connecting bar 18 can be converted into a rotation and thus a rotation of the eccentric spindle 4 with respect to the work spindle 6 can be realized.
For the adjustment the servomotor 8 is appropriately driven so that the adjusting slide 14 is moved free from play along its axial guide via the circulating ball spindle 12 and thus the connecting bar 18 immerses into the work spindle 6. The axial movement of the connecting bar 18 is converted into a rotation of the eccentric spindle 4 by the lift-off rotary transformer 20 so that, in response to the control of the step motor 8, the eccentric spindle 4 is adjusted so that the tool cutting edge is adjustable with respect to the work spindle 6.
The work spindle 6 is driven via a pulley 22 indicated by a dot-dash line, so that the cutting tool held in the tool holding fixture 2--for instance a boring tool--is rotated. As the components required for adjusting the cutting edge are substantially supported in the work spindle 6 or are connected with the same, considerable efforts have to be made to ensure the desired transmission free from play of the adjusting movement of the servomotor 8 to the eccentric spindle 4.
The system represented in FIG. 1 moreover has a very complex structure, because a multiple conversion of translatory movements into rotary movements is required. The moved masses are relatively large in the case of this feed system so that also the support of the work spindle and the motors required for the drive of the work spindle 6 have to be adequately designed.
In GB2130937A a feed system is described in which the cutting edge if fixed to an eccentric adapted to be rotated vis-a-vis a work spindle. The eccentric is adjusted by an adjusting shaft connected to a servomotor via a planetary gear. The transmission ratio of the planetary gear is selected to be such that the adjusting shaft automatically rotates with the work spindle in the basic setting. By driving the servomotor the adjusting shaft can be rotated via the planetary gear vis-a-vis the work spindle so that a feed motion is effected.
What is a drawback with this design is that a considerable expenditure in terms of apparatuses is necessary to couple the adjusting shaft via the planetary gear with the servomotor and to convert the motion of rotation of the adjusting shaft in the tool holding fixture into an adjustment of the eccentric.